1 files changed, 101 insertions, 0 deletions
diff --git a/libavfilter/vf_framestep.c b/libavfilter/vf_framestep.c
new file mode 100644
index 0000000..09945e1
--- /dev/null
+++ b/libavfilter/vf_framestep.c
@@ -0,0 +1,101 @@
+/*
+ * Copyright (c) 2012 Stefano Sabatini
+ *
+ * This file is part of FFmpeg.
+ *
+ * FFmpeg is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * FFmpeg is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with FFmpeg; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+/**
+ * @file framestep filter, inspired on libmpcodecs/vf_framestep.c by
+ * Daniele Fornighieri <guru AT digitalfantasy it>.
+ */
+
+#include "libavutil/opt.h"
+#include "avfilter.h"
+#include "internal.h"
+#include "video.h"
+
+typedef struct NullContext {
+    const AVClass *class;
+    int frame_step;
+} FrameStepContext;
+
+#define OFFSET(x) offsetof(FrameStepContext, x)
+#define FLAGS AV_OPT_FLAG_FILTERING_PARAM|AV_OPT_FLAG_VIDEO_PARAM
+
+static const AVOption framestep_options[] = {
+    { "step", "set frame step",  OFFSET(frame_step), AV_OPT_TYPE_INT, {.i64=1}, 1, INT_MAX, FLAGS},
+    { NULL },
+};
+
+AVFILTER_DEFINE_CLASS(framestep);
+
+static int config_output_props(AVFilterLink *outlink)
+{
+    AVFilterContext *ctx = outlink->src;
+    FrameStepContext *framestep = ctx->priv;
+    AVFilterLink *inlink = ctx->inputs[0];
+
+    outlink->flags |= FF_LINK_FLAG_REQUEST_LOOP;
+    outlink->frame_rate =
+        av_div_q(inlink->frame_rate, (AVRational){framestep->frame_step, 1});
+
+    av_log(ctx, AV_LOG_VERBOSE, "step:%d frame_rate:%d/%d(%f) -> frame_rate:%d/%d(%f)\n",
+           framestep->frame_step,
+           inlink->frame_rate.num, inlink->frame_rate.den, av_q2d(inlink->frame_rate),
+           outlink->frame_rate.num, outlink->frame_rate.den, av_q2d(outlink->frame_rate));
+    return 0;
+}
+
+static int filter_frame(AVFilterLink *inlink, AVFrame *ref)
+{
+    FrameStepContext *framestep = inlink->dst->priv;
+
+    if (!(inlink->frame_count % framestep->frame_step)) {
+        return ff_filter_frame(inlink->dst->outputs[0], ref);
+    } else {
+        av_frame_free(&ref);
+        return 0;
+    }
+}
+
+static const AVFilterPad framestep_inputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .filter_frame = filter_frame,
+    },
+    { NULL }
+};
+
+static const AVFilterPad framestep_outputs[] = {
+    {
+        .name         = "default",
+        .type         = AVMEDIA_TYPE_VIDEO,
+        .config_props = config_output_props,
+    },
+    { NULL }
+};
+
+AVFilter ff_vf_framestep = {
+    .name        = "framestep",
+    .description = NULL_IF_CONFIG_SMALL("Select one frame every N frames."),
+    .priv_size   = sizeof(FrameStepContext),
+    .priv_class  = &framestep_class,
+    .inputs      = framestep_inputs,
+    .outputs     = framestep_outputs,
+    .flags       = AVFILTER_FLAG_SUPPORT_TIMELINE_GENERIC,
+};